Conventionally, this type of apparatus for stabilizing power supply of heater housing box cooling apparatus has been applied not only in the heater housing box cooling apparatus, but also in the type having a plurality of taps provided in a power transformer designed to be changed over by detection of secondary side voltage. For instance, an example of this type of apparatus for stabilizing power supply of heater housing box cooling apparatus is disclosed in patent document 1.
The conventional apparatus for stabilizing power supply of heater housing box cooling apparatus is described below by reference to FIG. 11, FIG. 12, FIG. 13, and FIG. 14.
As shown in FIG. 11 to FIG. 14, heater housing box cooling apparatus 202 for cooling heater housing box 201 includes heat exchanger 203 as a heat exchanger for releasing an internal air to an external air, electronic controller 205 having first microcomputer 204 as a control unit, and direct-current fan motor 206 controlled and driven by electronic controller 205.
Alternating-current power supply 207 supplied from heater housing box 201 into heater housing box cooling apparatus 202 is connected in a primary winding of power transformer 208. Tap changeover relay 209 as 1C contact type relay is provided as a switch element as a tap changeover part for changing over a plurality of taps provided in a secondary winding of this power transformer 208. It is supposed herein that only one intermediate tap is provided.
A normally closed terminal of tap changeover relay 209 is connected to one terminal b of the secondary winding of power transformer 208, and a normally opened terminal of this tap changeover relay 209 is connected to intermediate tap c. A common terminal of tap changeover relay 209, and other terminal a of the secondary winding of power transformer 208 are connected to first diode bridge 210, and full waves are rectified, and smoothed by first capacitor 211, and produced as direct-current voltage V2, which is supplied to direct-current fan motor 206 and electronic controller 205.
In this configuration, from alternating-current voltage E2 applied to power transformer 208 from alternating-current power supply 207, direct-current voltage V2 of about √{square root over ( )}2 times of the output voltage determined by the turn ratio of the primary winding and the secondary winding of power transformer 208 is generated. Direct-current voltage V2 is divided by fourth resistor 212 and fifth resistor 213 as output voltage detectors for detecting the output voltage of power transformer 208, and is applied into analog input terminal AIN of first microcomputer 204. When the voltage of AIN exceeds a first threshold (for example, corresponding to 29 V at the voltage of direct-current voltage V2), immediately first microcomputer 204 commands relay drive circuit 214 to turn on tap changeover relay 209. Relay drive circuit 214 changes over the contact point of tap changeover relay 209 to the normally opened side, and the circuit is changed over in the direction of decreasing the number of turns of the secondary winding of power transformer 208, and the output voltage of the secondary side of power transformer 208 declines along with the turn ratio, and the value of direct-current voltage V2 is also lowered.
Afterwards, due to changes of alternating-current voltage E2 of alternating-current power supply 207 or the like, direct-current voltage V2 is also changed, and when the voltage of AIN becomes lower than a second threshold (for example, corresponding to 20 V at the voltage of direct-current voltage V2), immediately first microcomputer 204 commands relay drive circuit 214 to turn off tap changeover relay 209. Relay drive circuit 214 changes over the contact point of tap changeover relay 209 to the normally closed side, and the circuit is changed over in the direction of increasing the number of turns of the secondary winding of power transformer 208, and the output voltage of the secondary side of power transformer 208 climbs up along with the turn ratio, and the value of direct-current voltage V2 is also raised. In this manner, direct-current voltage V21 varies depending on the change of alternating-current voltage E2 of alternating-current power supply 207, but by operating tap changeover relay 209 depending on the value of direct-current voltage V2, the plurality of taps provided in power transformer 208 can be changed over, and the output voltage, that is, direct-current voltage V2 is controlled within a predetermined allowable voltage range (herein, 20 to 29 V).
The conventional apparatus for stabilizing power supply of heater housing box cooling apparatus is not only applied in the heater housing box cooling apparatus, but also available in a type having a plurality of taps provided in a power transformer for detecting the value of alternating-current voltage of the alternating-current power supply and selecting a proper tap depending on the detected voltage value. Such conventional apparatus for stabilizing power supply is disclosed, for example, in patent document 2.
Such conventional apparatus for stabilizing power supply of heater housing box cooling apparatus is described below by reference to FIG. 15 and FIG. 16.
As shown in FIG. 15 and FIG. 16, automatic changeover circuit 315 is provided between alternating-current power supply 307 to be supplied to heater housing box cooling apparatus 302 and power transformer 308. This automatic changeover circuit 315 detects alternating-current voltage E3 of alternating-current power supply 307, and selects a proper one of the plurality of taps provided in power transformer 308 depending on the detected voltage value, and supplies alternating-current voltage E3 to this tap. It is supposed herein that two intermediate taps are provided.
Automatic changeover circuit 315 is composed of tap selection relays 316a, 316b, 316c, input voltage detector 317 as input alternating-current voltage for detecting alternating-current voltage E3 of alternating-current power supply 307, and relay drive circuit 314. Relay drive circuit 314 selects a proper tap out of the plurality of taps provided in power transformer 308 depending on the voltage value detected by input voltage detector 317, and drives tap selection relays 316a to c so that the selected one may be connected to alternating-current power supply 307.
The secondary side of power transformer 308 is connected to first diode bridge 310, and full waves are rectified, and smoothed by first capacitor 311, and produced as direct-current voltage V3 of about √{square root over ( )}2 times of the output voltage determined by the turn ratio of the primary winding and the secondary winding of power transformer 308, and it is connected to direct-current fan motor 306 and electronic controller 305. Referring now to FIG. 16, input voltage detector 317 is more specifically described. This is the input alternating-current voltage detector for detecting the voltage value of alternating-current voltage E3 in a wide range from nominal voltage 200 V to 250 V. In input voltage detector 317, voltage transformer 318 is connected to alternating-current power supply 307, and the secondary side output voltage of voltage transformer 318 is rectified and smoothed by second diode bridge 319 and second capacitor 320. This rectified and smoothed direct-current voltage V4 is applied to analog input terminal MN of second microcomputer 321. The power supply of +5 V for driving second microcomputer 321 is created by converting direct-current voltage V4 by means of DC/DC converter 322.
In this configuration, when alternating-current power supply 307 is turned on, second microcomputer 321 commands relay drive circuit 314 so as to control tap selection relay 316c to close the contact if direct-current voltage V4 becomes lower than a third threshold (for example, corresponding to 220 V of alternating-current voltage E3), to control tap selection relay 316b to close the contact if direct-current voltage V4 becomes higher than the third threshold and lower than a fourth threshold (for example, corresponding to 240 V of alternating-current voltage E3), and to control tap selection relay 316a to close the contact if direct-current voltage V4 becomes higher than the fourth threshold.
Depending on this command, relay drive circuit 314 closes any one contact of tap selection relays 316a, 316b, 316c, and creates direct-current voltage V3. Later, depending on the change of alternating-current voltage E3 of alternating-current power supply 307, direct-current voltage V3 and direct-current voltage V4 are changed, and the closing contacts of tap selection relays 316a, 316b, 316c are changed over depending on the circumstances of the third threshold and the fourth threshold, and direct-current voltage V3 is controlled within a predetermined allowable voltage range (herein 20 to 29 V).
Further, if alternating-current voltage E3 of alternating-current power supply 307 exceeds the nominal voltage value due to trouble of the power distribution system or the like, and direct-current voltage V4 becomes an overvoltage exceeding a fifth threshold (for example, corresponding to 275 V of alternating-current voltage E3), all contacts of tap selection relays 316a, 316b, 316c are opened. Power transformer 308 is cut off from alternating-current power supply 307, and it is intended to protect from overvoltage so as not to breakdown heater housing box cooling apparatus 302 due to direct-current voltage V3 exceeding the allowable voltage range.
In such conventional apparatus for stabilizing power supply of heater housing box cooling apparatus for changing over the plurality of taps provided in the power transformer depending on detection of secondary side voltage, when the alternating-current power supply is turned on, in less than a second, an output voltage determined by the turn ratio of the primary winding and the secondary winding of the power transformer is generated. This output voltage is generated before the electronic controller detects the output voltage value and operates to select the tap. Thus, the operation of the tap changeover relay is delayed, and for several seconds at least, the connection is fixed to one of the plurality of taps provided in the power transformer. Therefore, the output voltage determined by the turn ratio of the primary winding and the secondary winding of the power transformer is fixed for several seconds and cannot be controlled, possibly exceeding the allowable voltage range depending on the input value of the alternating-current voltage. It is hence required to control so as not to induce breakage of the direct-current fan motor or the electronic controller connected to the output voltage due to the output voltage of the power transformer exceeding the allowable voltage range.
An easy method of preventing breakage by exceeding the allowable output voltage range is to design in a wider allowable applied voltage of the direct-current fan motor or the electronic controller to be connected. That is, it may be considered to select a component one rank higher in the dielectric strength, or to provide each device with an overvoltage preventive circuit. In these methods, however, the apparatus may be increased in size or raised in cost unnecessarily, and it has been demanded to decrease the size of the apparatus while solving these problems.
When turning on the alternating-current power supply, a large rush current flows as excitation current of the power transformer, and it is necessary to prepare a sufficient power supply capacity of the alternating-power supply. In other words, the facility cannot be used unless the power supply capacity is sufficient, and it is demanded to suppress the excitation current of the power transformer occurring at the time of turning on the alternating-current power supply.
In the conventional apparatus for stabilizing power supply of heater housing box cooling apparatus by detecting the value of the output voltage of the alternating-current power supply, and selecting a proper tap out the plurality of taps provided in the power transformer depending on the detected voltage value, as the input alternating-current voltage detector for detecting the voltage value of the alternating-current voltage, for the overvoltage exceeding the nominal voltage value generate due to trouble of the power distribution system or the like, the input voltage detector itself may be exposed to an overvoltage. It is hence demanded to control so that the input voltage detector may not be broken by overvoltage of the alternating-current power source.
As an easy method of preventing breakage of input voltage detecting device due to overvoltage of the alternating-current power supply, it may be considered to select a component one rank higher in the dielectric strength, or to provide each device with an overvoltage preventive circuit. In these methods, however, the apparatus may be increased in size or raised in cost unnecessarily, and it has been demanded to decrease the size of the apparatus while solving these problems.
Besides, since the since the tap of the power transformer and the alternating-current power supply are connected only when detecting the value of the alternating-current voltage of the alternating-current power supply, in order to execute various operations in the automatic changeover circuit, the power supply cannot be supplied from the output voltage of the power transformer, and it was required to compose a power supply circuit separately inside or outside of the automatic changeover circuit. It has been demanded to decrease the apparatus in size by solving these problems.
At the time of overvoltage of alternating-current power supply, the power feed to the power transformer is cut off, and the electronic controller, which is the core of the cooling apparatus operating by the output voltage of the power transformer, cannot be operated. Accordingly, in the event of overvoltage of alternating-current power supply, it is required to assure power feeding to the electronic controller.
Also at the time of overvoltage of alternating-current power supply, it is impossible to report overvoltage protective operation to outside, and it is required to report overvoltage protective operation to outside in the event of overvoltage of alternating-current power supply.    Patent document 1: Japanese Patent Unexamined Publication No. H5-109172.    Patent document 2: Japanese Patent Unexamined Publication No. H11-155135.